Optimization design method for length of tunnel plug in main flood season of extra-high dam construction

Abstract

The invention relates to the technical field of water conservancy and hydropower engineering construction, discloses an optimal design method for the length of a tunnel plug in the main flood season of extra-high dam construction, and solves the problems that in a design scheme of the length of the tunnel plug in the traditional technology, the project investment is increased, the construction period is prolonged, and the reliability analysis of the tunnel plug is not comprehensive enough. The method comprises the following steps: firstly, determining a tunnel control sliding interface through engineering basic parameter analysis, and initially simulating the length of a tunnel plug; then building an anti-sliding stable failure risk model of the tunnel plug in the main flood season of the ultra-high dam construction; then determining distribution parameters of main random factors influencing the water load and the anti-sliding force; then, based on the initially planned length of the tunnel plug, in combination with distribution parameters of main random factors influencing the water load and the anti-sliding force, random simulation of the water load generated by the maximum flood level of dam flood control in the main flood season and the total anti-sliding force generated by the tunnel plug is carried out; according to the stochastic simulation result, the anti-sliding stability failure risk rate of the plug is estimated; and finally, according to the estimated anti-sliding stability failure risk rate, optimizing the length of the tunnel plug until the convergence condition is met.

Description

Technical Field

[0001] The invention relates to the technical field of water conservancy and hydropower engineering construction, and in particular to a method for optimizing the design of tunnel plug length during the main flood season for ultra-high dam construction. Background Art

[0002] Ultra-high dams are mostly built in the mountainous canyon areas of the southwest region. Their construction diversion generally adopts a tunnel diversion method with a cofferdam to cut off the flow once and the foundation pit to be constructed throughout the year. The construction of ultra-high dam hydropower projects is difficult and has a long construction period. The construction process is affected by many uncertain factors. The calculation and analysis of the plugging stability of tunnels such as hydraulics, transportation, construction branches, and temporary construction passages has always been a key technical issue in the design and research of underground engineering for large hydropower stations. With the continuous advancement of the construction of ultra-high dam hydropower projects in the southwest region, more and more ultra-high dams are facing the safety and stability of plugging structures such as construction tunnels and hydraulic tunnels under the conditions of flood season. For example, the lining of the ecological water supply tunnel of a 300m-class ultra-high core wall rockfill dam was not completed before the flood season, and it was necessary to arrange plugging of the construction branch tunnel to ensure that there was no water in the water supply tunnel during the main flood season of that year and the construction was safe.

[0003] At present, the conventional method for engineering and technical personnel to design the length of hydraulic tunnel plug structures is mainly to first preliminarily estimate the length, then use the overall anti-sliding stability method, shear resistance calculation method, empirical design method, etc. to conduct stability verification, and finally determine the plug length based on experience. These methods are simple in principle and easily accepted by engineering designers.

[0004] However, the above-mentioned design method of the plug length cannot reflect the influence of major random factors such as rock mechanical parameters, concrete parameters and contact coefficient between sliding surface materials on the structural stability. The calculation results are conservative, which not only increases the project investment, but also prolongs the construction and demolition period.

[0005] In recent years, with the development of hydraulic reliability theory, the application of limit state design method based on probability theory in engineering design has been continuously deepened. Wang Kui et al. considered the influence of geotechnical engineering uncertainty factors and introduced reliability theory to calculate and analyze the stability of permanent plugs in hydraulic tunnels. However, for the tunnel plug structure used to retain water during the main flood season, the model is mainly aimed at circular hydraulic tunnels, and is difficult to apply to the gate-type tunnels that are widely used; on the other hand, the model ignores the influence of the randomness of the upstream water pressure load during the flood season, making the reliability analysis of the tunnel plug not comprehensive enough.

[0006] In addition, there is currently no report on a method for optimizing the length of tunnel plugs based on risk design. In view of this, the present invention takes into account the influence of major random factors and studies a method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction based on risk analysis theory, in order to provide a scientific theoretical basis and technical support for determining an appropriate scale of tunnel plugging projects, thereby reducing project investment, ensuring construction safety during flood seasons, and accelerating project progress. Summary of the invention

[0007] The technical problem to be solved by the present invention is to propose a method for optimizing the design of the tunnel plug length during the main flood season of ultra-high dam construction, so as to solve the problems of increased project investment, extended construction period and incomplete reliability analysis of the tunnel plug in the design scheme of the tunnel plug length in the traditional technology.

[0008] The technical solution adopted by the present invention to solve the above technical problems is:

[0009] The optimization design method of tunnel plug length during the main flood season of ultra-high dam construction includes the following steps:

[0010] S1. Determine the controlled sliding interface of the tunnel through the analysis of basic engineering parameters and preliminarily estimate the length of the tunnel plug;

[0011] S2. Establish a risk model for the failure of tunnel plugging resistance during the main flood season of ultra-high dam construction;

[0012] S3. Determine the distribution parameters of the main random factors affecting water load;

[0013] S4. Determine the distribution parameters of the main random factors affecting the anti-slip force;

[0014] S5. Based on the initially proposed tunnel plug length and the distribution parameters of the main random factors affecting water load and anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is conducted;

[0015] S6. Estimate the risk rate of failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction based on random simulation results;

[0016] S7. Based on the estimated risk rate of failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction, optimize the length of tunnel plugs until the convergence conditions are met.

[0017] Furthermore, in step S1, the tunnel control sliding interface is determined through the analysis of basic engineering parameters, and the tunnel plug length is initially estimated, including:

[0018] Determine the tunnel plugging design level and flood control standards according to the relevant hydraulic tunnel design specifications;

[0019] Determine the controlled sliding interface of the tunnel: For unlined tunnels, the interface between concrete and surrounding rock is used as the controlled sliding interface; for lined tunnels, the fixed value method is used to calculate the anti-sliding stability of the interface between the plug and concrete as the sliding surface and the interface between concrete and surrounding rock as the sliding surface under the most unfavorable working conditions, and the controlled sliding interface is determined based on the anti-sliding stability;

[0020] Combined with the design parameter values ​​of tunnel plugging design level and flood control standard and the controlling sliding interface, the partial factor limit state design method is adopted to estimate the tunnel plugging length.

[0021] Furthermore, in step S2, the established risk model for the anti-sliding stability failure of the tunnel plug during the main flood season of the ultra-high dam construction is:

[0022] R=P(P H (max(Z m (t)))>f'∑W+C'(λA1+A2))

[0023] Among them, R represents the risk of failure of anti-sliding stability of tunnel plugging during the main flood season of ultra-high dam construction; Z m (t) represents the dynamic change process of the water level of the reservoir in front of the dam during the main flood season; P H (max(Z m (t))) is the thrust of the water load generated by the highest flood level on the upstream face of the plug; f' is the shear friction coefficient between the plug and the surrounding rock; ∑W is the sum of all normal forces on the control sliding surface; C' is the cohesion between the plug and concrete or between concrete and surrounding rock; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of ​​the side wall; A2 is the effective shear surface contact area of ​​the bottom surface; P(·) represents the probability that the (·) condition is met.

[0024] Furthermore, in step S3, the distribution parameters of the main random factors affecting the water load are determined to include:

[0025] The construction flood peak is assumed to follow the P-III type distribution;

[0026] The discharge capacity coefficient of the diversion tunnel is assumed to follow a triangular distribution;

[0027] The water level-reservoir capacity relationship coefficient is assumed to obey a triangular distribution.

[0028] Furthermore, in step S4, the distribution parameters of the main random factors affecting the anti-slip force are determined, including:

[0029] The effective bonding area coefficient of the side wall is assumed to obey a triangular distribution, and its probability density function is:

[0030]

[0031] Among them, k d is the lower limit, i.e. the minimum effective bonding area coefficient of the side wall; k m is the median value, estimated based on the technical level of the construction unit and on-site management; k u is the upper limit value, i.e. the maximum bonding effective area coefficient of the side wall;

[0032] The shear friction coefficient and cohesion of the plug material are assumed to obey the normal distribution, and their probability density functions are:

[0033]

[0034] Wherein, μ is the mean of the random variable parameter of the shear friction coefficient f' or the cohesion C'; σ is the standard deviation of the random variable parameter of the shear friction coefficient f' or the cohesion C'.

[0035] Furthermore, in step S5, based on the initially proposed tunnel plug length and in combination with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that can be generated by the tunnel plug is performed, including:

[0036] First, the total number of model simulation calculations N that meets the calculation accuracy requirements is determined based on the Monte Carlo method. C ;

[0037] Then, combining the distribution parameters of the main random factors affecting water load and anti-sliding force, N C Random simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plug.

[0038] Furthermore, the random simulation process of the water load generated by the highest flood level of the dam during the main flood season includes:

[0039] ① Generate random numbers of construction flood peaks to simulate the construction flood process;

[0040] ② Generate random numbers of reservoir capacity relationship coefficients and simulate and fit the water level capacity relationship curve;

[0041] ③ Generate random numbers of discharge capacity coefficients and simulate and fit the diversion and discharge capacity curve;

[0042] ④ The maximum flood level in front of the dam during the main flood season is obtained by simulating flood control calculations. m (t));

[0043] ⑤ Calculate the water load P by simulating the highest flood level in front of the dam during the main flood season H (max(Z m (t))).

[0044] Furthermore, the random simulation process of the total anti-sliding force that can be generated by the tunnel plug includes:

[0045] ① Generate a random number for the bonding effective area coefficient λ of the side wall;

[0046] ② Generate random numbers of shear friction coefficient f' and cohesion C';

[0047] ③ Calculate the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate.

[0048] Furthermore, in step S6, based on the random simulation results, the risk rate of failure of the anti-sliding stability of the tunnel plug during the main flood season of the ultra-high dam construction is estimated, including:

[0049] According to N C The simulation results of random simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plugging are analyzed statistically. The water load P of the highest flood level in front of the dam is H (max(Z m The number of times (t))) exceeds the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate is recorded as N T ;

[0050] According to Estimate the risk rate R of anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction.

[0051] Further, in step S7, according to the estimated risk rate of failure of the tunnel plugging anti-sliding stability during the main flood season of the ultra-high dam construction, the length of the tunnel plugging is optimized until the convergence condition is met, including:

[0052] Determine whether the estimated risk rate R of tunnel plugging anti-sliding stability failure during the main flood season of ultra-high dam construction meets the following requirements:

[0053] 0≤|RR A |≤ε

[0054] Among them, R A is the design risk rate, R A =1 / T A , T A is the flood return period corresponding to the tunnel plugging design standard; ε is the set convergence threshold;

[0055] If satisfied, the optimization design process is terminated; otherwise, the length of the tunnel plug is adjusted. Based on the adjusted length of the tunnel plug and the distribution parameters of the main random factors affecting water load and anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is performed again, and then the process returns to step S6.

[0056] The beneficial effects of the present invention are:

[0057] (1) The present invention introduces risk analysis theory and methods to construct a mathematical model for the risk of anti-sliding stability failure of ultra-high dam tunnel plugs before flood season, taking into account the randomness of the main factors affecting water load and the randomness of the main factors affecting anti-sliding force. It is more in line with the objective reality of the project and is more suitable for the optimal design of tunnel plugs during the main flood season of ultra-high dam construction.

[0058] (2) In the optimization design of the tunnel plugging during the main flood season of the ultra-high dam construction, the present invention adopts a risk analysis method based on probability theory, scientifically and reasonably and comprehensively considers the influence of the randomness of various random factors, and improves the scientificity and accuracy of risk rate estimation and analysis.

[0059] (3) By adopting the optimized design scheme of the present invention, the scale of the tunnel plugging project can be reduced while ensuring a certain degree of anti-slip stability and reliability of the plugging, thereby reducing the investment in the plugging project and shortening the construction period, which has good social, economic and safety benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 The present invention is a flow chart of the method for optimizing the design of tunnel plug length during the main flood season for ultra-high dam construction. DETAILED DESCRIPTION

[0061] The present invention aims to provide a method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction, so as to solve the problems of increased engineering investment, extended construction period and insufficient reliability analysis of tunnel plugs in the design scheme of tunnel plug length in traditional technology. The present invention first determines the tunnel control sliding interface through the analysis of basic engineering parameters, and preliminarily proposes the length of tunnel plugs; then establishes a risk model for the anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction; then systematically analyzes the randomness of the main factors affecting water load and anti-sliding force, and determines the distribution parameters of the main random factors; then, based on the preliminarily proposed tunnel plug length, combined with the distribution parameters of the main random factors affecting water load and anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam flood control during the main flood season and the total anti-sliding force that can be generated by the tunnel plug is performed; and according to the random simulation results, the risk rate of anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction is estimated; finally, according to the estimated risk rate of anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction, the length of tunnel plugs is optimized until the convergence condition is met. This design method provides a scientific theoretical basis and technical support for determining the appropriate scale of tunnel plugging projects, thereby reducing project investment, ensuring construction safety during flood seasons, and accelerating project progress.

[0062] For specific implementation, see Figure 1 The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction provided by the present invention comprises the following implementation steps:

[0063] S1. Determine the controlled sliding interface of the tunnel through the analysis of basic engineering parameters and preliminarily estimate the length of the tunnel plug;

[0064] In this step, the tunnel plugging design level and flood control standard are determined according to the relevant design specifications for hydraulic tunnels;

[0065] And according to the actual project, determine the tunnel control sliding interface:

[0066] For unlined tunnels, the interface between concrete and surrounding rock is used as the controlling sliding interface;

[0067] For lined tunnels, the fixed value method is used to calculate the anti-sliding stability of the interface between the plug and concrete as the sliding surface and the interface between concrete and surrounding rock as the sliding surface under the most unfavorable working conditions, and the controlled sliding interface is determined based on the anti-sliding stability.

[0068] Finally, combined with the design parameter values ​​of the tunnel plug design level and flood control standard and the controlled sliding interface, the partial factor limit state design method is used to estimate the tunnel plug length L0, which serves as the initial input condition for the subsequent calculation of the anti-sliding stability failure risk of the plug.

[0069] S2. Establish a risk model for the failure of tunnel plugging resistance during the main flood season of ultra-high dam construction;

[0070] In this step, according to the hydraulic structure theory and in combination with relevant regulations and specifications, taking the gate-type tunnel plug, which is the most widely used in hydropower projects, as an example, the sliding of the tunnel plug along the interface is the main structural failure mode of the tunnel plug. The load effect of the tunnel plug is mainly the thrust of the water load generated by the highest construction flood level on the upstream face of the plug, and the structural resistance is the friction between the plug and the concrete or between the concrete and the surrounding rock and the cohesion of the material. Based on this, the anti-sliding stability limit state equation of the tunnel plug during the main flood season of the super-high dam construction can be described as:

[0071] Z=P H (max(Z m (t)))-(f'∑W+C'(λA1+A2))=0

[0072] Among them, Z m (t) is the dynamic change process of the water level of the reservoir in front of the dam during the main flood season; P H (max(Z m(t))) is the thrust of the water load generated by the highest flood level on the upstream side of the plug; f' is the shear friction coefficient between the plug and concrete or between concrete and surrounding rock; ∑W is the sum of all normal forces on the sliding surface, unit MN; C' is the cohesion between the plug and concrete or between concrete and surrounding rock, unit MPa; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of ​​the side wall, unit m 2 ; A2 is the effective shear contact area of ​​the bottom surface, unit: m 2 .

[0073] After research, it was found that the risk of structural sliding failure of tunnel plugs during the construction flood season is mainly affected by the combined influence of random factors such as hydrology, hydraulics, and material mechanics parameters. Among them, the water load generated by the highest water level in the upstream reservoir is affected by random factors such as hydrology, hydraulics, and the relationship between water level and storage capacity, and has a certain randomness; the randomness of material mechanics parameters makes the total anti-sliding force of the plug have a certain randomness. The present invention defines the risk of anti-sliding stability failure of the plug during the main flood season of ultra-high dam construction as the probability of the tunnel plug suffering from anti-sliding stability failure due to the water load generated by the highest upstream flood level during the main flood season. Therefore, taking into account the randomness of the main influencing factors, the mathematical model of the anti-sliding stability failure risk R of the ultra-high dam tunnel plug before the flood season is established:

[0074] R=P(P H (max(Z m (t)))>f'∑W+C'(λA1+A2))

[0075] Among them, R represents the risk of failure of anti-sliding stability of tunnel plugging during the main flood season of ultra-high dam construction; Z m (t) represents the dynamic change process of the water level of the reservoir in front of the dam during the main flood season; P H (max(Z m (t))) is the thrust of the water load generated by the highest flood level on the upstream face of the plug; f' is the shear friction coefficient between the plug and the surrounding rock; ∑W is the sum of all normal forces on the control sliding surface; C' is the cohesion between the plug and concrete or between concrete and surrounding rock; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of ​​the side wall; A2 is the effective shear surface contact area of ​​the bottom surface; P(·) represents the probability that the (·) condition is met.

[0076] S3. Determine the distribution parameters of the main random factors affecting water load;

[0077] In this step, the distribution parameters of the main random factors affecting the water load are determined by systematically analyzing the randomness of the main factors affecting the water load. The water load generated by the highest flood level is the only load on the plug structure. The cofferdam storage capacity of the super-high dam hydropower project is generally large, and the regulation and storage effect is more obvious. The highest flood level in front of the dam during the main flood season is affected by the hydrological and hydraulic randomness and has a large randomness, specifically:

[0078] (1) Randomness of construction flood process:

[0079] The construction flood process is random due to the randomness of precipitation in the catchment area upstream of the dam and the randomness of the catchment time. At present, the simulation of the construction flood process is basically based on the simulation of the flood peak, that is, the randomness of the construction flood peak is the basis for the simulation of the construction flood process. Therefore, in order to facilitate calculation and analysis, the hydrological random factors mainly consider the randomness of the peak, assuming its P-Ⅲ type distribution. On the basis of determining the probability distribution model of the construction flood peak, the construction flood process is determined by the method of amplifying the typical flood process according to the peak flow value.

[0080] (2) Randomness of diversion tunnel discharge capacity:

[0081] The flood discharge capacity of the construction diversion tunnel is affected by many random factors such as the tunnel cross-sectional area, wetted perimeter and bottom slope. The discharge capacity density function curve is obtained through random simulation, and then the goodness of fit between the normal distribution and the triangular distribution is compared. It is believed that the discharge capacity of the diversion tunnel is closer to the triangular distribution.

[0082] (3) Randomness of water level and storage capacity relationship:

[0083] Considering the influence of factors such as slope collapse and construction slag in the reservoir area, the actual water level and storage capacity relationship is also random, and the reservoir storage capacity relationship coefficient is also assumed to obey the triangular distribution.

[0084] S4. Determine the distribution parameters of the main random factors affecting the anti-slip force;

[0085] In this step, the distribution parameters of the main random factors affecting the anti-slip force are determined by systematically analyzing the randomness of the main factors affecting the anti-slip force, specifically:

[0086] (1) Randomness of side wall contact coefficient:

[0087] The effective bonding area coefficient of the side wall of the city gate tunnel plug affects the anti-slip force provided by the side wall of the plug, and then affects the total anti-slip force of the plug. However, affected by many uncertain factors such as concrete shrinkage, concrete pouring quality, grouting technology level, on-site construction management, and construction equipment, the effective bonding area coefficient of the side wall has a certain randomness. According to the specific conditions of the project, 0.3 to 0.8 is generally used. Since the value is within a certain range, and in actual projects, the technical strength of the construction unit and the on-site management situation can be combined to give a preference for good or bad structural construction quality, the coefficient for good construction quality is large, and the contact coefficient for poor construction quality is small. Therefore, it is assumed that the effective bonding area coefficient λ of the side wall follows a triangular distribution, and its probability density function is:

[0088]

[0089] Among them, k d is the lower limit, i.e. the minimum effective bonding area coefficient of the side wall; k m is the median value. The design is estimated based on the technical level of the construction unit and the on-site management. A larger value can be taken for good construction quality and a smaller value can be taken for poor construction quality. u It is the upper limit value, that is, the maximum bonding effective area coefficient of the side wall.

[0090] (2) Randomness of material parameters:

[0091] According to the anti-sliding stability limit equation, the main material parameters affecting the total resistance are the random variable parameters of the shear friction coefficient f' and the cohesion C'. Their distributions are assumed to obey the normal distribution, and their probability density functions are:

[0092]

[0093] Wherein, μ is the mean of the random variable parameter of the shear friction coefficient f' or the cohesion C'; σ is the standard deviation of the random variable parameter of the shear friction coefficient f' or the cohesion C'.

[0094] S5. Based on the initially proposed tunnel plug length and the distribution parameters of the main random factors affecting water load and anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is conducted;

[0095] In this step, the total number of model simulation calculations N that meets the calculation accuracy requirements is first determined based on the Monte Carlo method. C ; Then, combined with the distribution parameters of the main random factors affecting water load and anti-sliding force, N C Random simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plug.

[0096] The random simulation process of the water load generated by the highest flood level of the dam during the main flood season includes:

[0097] ① Generate random numbers of construction flood peaks to simulate the construction flood process;

[0098] ② Generate random numbers of reservoir capacity relationship coefficients and simulate and fit the water level capacity relationship curve;

[0099] ③ Generate random numbers of discharge capacity coefficients and simulate and fit the diversion and discharge capacity curve;

[0100] ④ The maximum flood level in front of the dam during the main flood season is obtained by simulating flood control calculations. m (t));

[0101] ⑤ Calculate the water load P by simulating the highest flood level in front of the dam during the main flood season H (max(Z m (t))).

[0102] The random simulation process of the total anti-sliding force that the tunnel plug can generate includes:

[0103] ① Generate a random number for the bonding effective area coefficient λ of the side wall;

[0104] ② Generate random numbers of shear friction coefficient f' and cohesion C';

[0105] ③ Calculate the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate.

[0106] Based on the above simulation process, we can get N C The random simulation results of the water load generated by the highest flood level of the dam during the main flood season and N C Simulation results of the total anti-sliding force that a tunnel plug can generate.

[0107] S6. Estimate the risk rate of failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction based on random simulation results;

[0108] In this step, according to N C The simulation results of random simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plugging are analyzed statistically. The water load P of the highest flood level in front of the dam is H (max(Z m The number of times (t))) exceeds the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate is recorded as N T ;

[0109] According to Estimate the risk rate R of anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction.

[0110] S7. Based on the estimated risk rate of failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction, optimize the length of tunnel plugs until the convergence conditions are met.

[0111] In this step, the risk theory method is used to identify the risk of the plug length design scheme. Assume that the flood return period corresponding to the tunnel plug design standard is T A , converted to the design risk rate R A , the calculation expression is:

[0112] R A =1 / T A

[0113] Therefore, the risk judgment criteria for the tunnel plug length design scheme to meet the requirements of the specification are:

[0114] R≤R A

[0115] Based on the initial tunnel plug L0 design scheme, R is obtained according to the above diversion risk rate estimation method, and according to the risk judgment criterion, ε is given as a very small positive number, and the inequality condition 0≤|RR A |≤ε is used as the convergence condition of the optimization design to determine whether iterative convergence is satisfied. If satisfied, the design optimization process is exited; otherwise, the length of the tunnel plug is continuously adjusted, and the random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is performed again, and then the process returns to step S6 to continue calculating the anti-sliding stability failure risk rate until the convergence condition is satisfied.

[0116] Example

[0117] Taking the application of the solution of the present invention to the SJK Hydropower Station, a super-high core rockfill dam in the upper reaches of the Dadu River in China, as an example, an exemplary description of the optimization design method for the tunnel plug length during the main flood season is given.

[0118] The SJK Hydropower Station is a control reservoir in the upper reaches of the Dadu River Basin in China. The dam is a super-high core rockfill dam with a height of 315.00m, which is currently the highest dam in the world. The project is a first-class large (1) type project. The hub project consists of a dam, flood discharge structures, and a water diversion and power generation system. The valley slope of the project is steep and the bedrock is exposed. The project adopts a tunnel diversion method with a cofferdam to cut off the flow once and the foundation pit to be constructed throughout the year.

[0119] The project takes into account ecological water supply, maintenance, emergency, etc., and specially designs an ecological water supply tunnel during the construction period, and the project level is 3. Affected by various complex factors such as on-site management and emergencies, the progress of the project construction has been seriously delayed. According to the actual progress of the project, the pre-flood filling elevation of the dam in a certain year reached 2316.00m, exceeding the upstream cofferdam by 2308.00m, and the flood standard of the dam is a once-in-100-year standard. However, the ecological water supply tunnel is still in the stage of concrete lining in the tunnel. The project needs to rush to carry out concrete construction lining during the flood season. In order to ensure that after the water level rises during the main flood season, floods will not enter the ecological water supply tunnel to cause structural damage and damage, and to ensure the safety of construction personnel and equipment in the tunnel, it is necessary to set a tunnel water retaining plug upstream. In order to determine the reasonable value of the plug, the solution provided in the present invention is implemented as follows:

[0120] 1. Initial proposed tunnel plug length:

[0121] According to the relevant regulations and specifications "Specifications for the Design of Hydraulic Tunnels" (NB / T 10391-2020), the plugging body of the tunnel construction branch should be consistent with the level of the tunnel building. Therefore, the plugging level of this tunnel is level 3, the flood standard for water retention is once in 20 years, and the design flood level is 2294.50m. The cross-section of the construction branch tunnel is 7.0m×8.0m, and the bottom elevation of the plugging body layout is 2259.00, from which it can be known that the working head is 35.5m.

[0122] Since the branch tunnel of this project is not lined, the interface between concrete and surrounding rock is taken as the controlled sliding surface. The partial factor limit state design method is used to calculate the tunnel plug length, which is initially planned to be 14.46m.

[0123] 2. Establish a risk model for the failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction:

[0124] The sliding of the tunnel plugging body along the interface is the main structural failure mode of the tunnel plug. The load effect of the tunnel plug is mainly the thrust of the water load generated by the highest construction flood level on the upstream face of the plug. The structural anti-sliding force is the friction between the concrete and the surrounding rock and the cohesion of the material. The anti-sliding stability limit state equation of the tunnel plug during the main flood season of the super-high dam construction is established as:

[0125] Z=P H (max(Z m (t)))-(f'∑W+C'(λA1+A2))=0

[0126] Among them, Z m (t) is the dynamic change process of the water level of the reservoir in front of the dam during the main flood season; P H (max(Z m(t))) is the thrust of the water load generated by the highest flood level on the upstream side of the plug; f' is the shear friction coefficient between the plug concrete and the surrounding rock; ∑W is the sum of all normal forces on the sliding surface, unit MN; C' is the cohesion between the plug and concrete or between concrete and surrounding rock, unit MPa; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of ​​the side wall, unit m 2 ; A2 is the effective shear contact area of ​​the bottom surface, unit: m 2 .

[0127] The tunnel plugging during the main flood season of this project is subject to the combined influence of random factors such as hydrology, hydraulics, and material mechanical parameters, and there is a risk of structural sliding failure. Among them, the water load generated by the highest water level in the upstream reservoir is subject to a certain degree of randomness due to the influence of random factors such as hydrology, hydraulics, and water level-reservoir capacity; the randomness of material mechanical parameters makes the total resistance of the plugging have a certain degree of randomness. Taking into account the randomness of the main influencing factors, the mathematical model of the anti-sliding stability failure risk R of the ultra-high dam tunnel plugging before the flood season is established:

[0128] R=P(P H (Z m (t))>f'∑W+C'(λA1+A2))

[0129] Among them, P(·) represents the probability that the (·) condition is true.

[0130] 3. Conduct a systematic analysis of the randomness of the main factors affecting water load and determine the distribution parameters of each random factor:

[0131] (1) Hydrological random parameters:

[0132] Based on the measured annual maximum flow series of the hydrological station, the investigated annual historical floods are added to form a discontinuous series for frequency calculation. The empirical frequencies of historical floods and measured series are calculated according to the expectation formula, the moment method is used to calculate the initial estimated parameters, and the eye estimation line fitting method is used to determine the hydrological random parameter as μ Q =2540m 3 / s,C v =0.33,C s / C v =5.0.

[0133] (2) Hydraulic random parameters:

[0134] The initial cross-sectional dimensions of the diversion tunnel are 15.0m×19.0m, and the discharge capacity coefficient of the discharge structure obeys a triangular distribution, with a value range generally between 0.97 and 1.05. Based on the experience of similar projects, the distribution parameter values ​​are 0.97 (lower limit), 1.00 (median value), and 1.05 (upper limit), respectively.

[0135] (3) Random parameters of water level and storage capacity relationship coefficient:

[0136] Considering that the water level-reservoir capacity relationship coefficient of the project follows a triangular distribution, and referring to relevant engineering experience, its distribution parameters are 0.99 (lower limit), 1.00 (median value), and 1.01 (upper limit).

[0137] 4. Conduct a systematic analysis of the randomness of the main factors affecting resistance and determine the distribution parameters of each random factor:

[0138] (1) Random parameter analysis of side wall contact coefficient:

[0139] The side wall contact coefficient follows a triangular distribution and generally ranges from 0.3 to 0.8. Based on the experience of similar projects and the construction management and technical level of the construction unit of this project, the median of the random distribution parameter of the side wall contact coefficient is taken as 0.5. Finally, the distribution parameter values ​​of the side wall contact coefficient λ are determined to be 0.3 (lower limit), 0.5 (median value), and 0.8 (upper limit).

[0140] (2) Material random parameter analysis:

[0141] The plugging concrete grade is C25, the surrounding rock grade is IV, and referring to relevant data and combining the construction site conditions, the statistical characteristics of the random parameters of the materials are shown in Table 1:

[0142] Table 1 Statistical characteristics of random parameters of materials

[0143] random variable Mean Coefficient of variation Distribution Type f' 0.7 0.2 Normal C' 0.4 0.1 Normal

[0144] 5. Carry out random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force generated by the tunnel plug, and optimize the design of the plug length:

[0145] Determine the total number of model simulation calculations that meet the calculation accuracy requirements, conduct random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate, simulate and calculate the anti-sliding stability failure risk rate R of the tunnel plug during the main flood season of the ultra-high dam construction, and optimize the plug length design until 0≤|RR is met A |≤ε.

[0146] To ensure the calculation accuracy, when the number of simulations is greater than 100,000 times, the calculation results tend to be stable and small. Therefore, the total number of design simulations is 100,000 times. When the length of the plug was initially proposed to be 14.46m, after 100,000 simulation calculations, it was found that the number of anti-sliding stability failures of the plug due to the water load at the highest flood level in front of the dam exceeding the total anti-sliding force that the tunnel plug can generate was 24 times, and the failure risk R was 0.24%, indicating that the initially proposed plug length has a high safety reliability, but the failure risk R is much less than the design risk rate of 5% of the 20-year design standard, which also shows that the traditional direct use of the partial factor limit state design method to estimate the plug length design is conservative.

[0147] By continuously readjusting the length of the plug, re-conducting random simulations of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate, and recalculating the risk rate of anti-sliding stability failure, it was finally found that when the design length of the plug was 3.35m, the number of anti-sliding stability failures of the plug was 5012 times, that is, the failure risk R was 5.012%, which is slightly greater than and very close to the standard of once in 20 years recurrence period.

[0148] Therefore, for this project, when using the risk-based structural design method, the length of the tunnel plug can be 3.35m, which can meet the requirements of flood control during the main flood season. Compared with the traditional design method of 14.46m, the length of the water retaining plug determined by this scheme is greatly shortened, so the project cost can be saved. Since 13 tunnel plugs are used in this project, it is estimated that the project cost savings are as high as several million yuan. In addition, the use of shorter water retaining plugs can speed up the construction progress while ensuring the anti-slip stability reliability that meets the design requirements.

[0149] Finally, it should be noted that the above embodiments are only preferred implementations and are not intended to limit the present invention. It should be pointed out that for those skilled in the art, several modifications, equivalent replacements, improvements, etc. can be made without departing from the scope of the present invention and the scope of protection of the claims, and all of these should be included in the protection scope of the present invention.

Claims

1. A method for optimizing the length of tunnel plugging during the main flood season of ultra-high dam construction, characterized in that: The following steps are involved: S1. Determine the controlled sliding interface of the tunnel through the analysis of basic engineering parameters and preliminarily estimate the length of the tunnel plug; S2. Establish a risk model for the failure of tunnel plugging resistance during the main flood season of ultra-high dam construction; S3. Determine the distribution parameters of the main random factors affecting water load; S4. Determine the distribution parameters of the main random factors affecting the anti-slip force; S5. Based on the initially proposed tunnel plug length and the distribution parameters of the main random factors affecting water load and anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is conducted; S6. Estimate the risk rate of failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction based on random simulation results; S7. Based on the estimated risk rate of failure of anti-sliding stability of tunnel plugs during the main flood season of ultra-high dam construction, optimize the length of tunnel plugs until the convergence conditions are met.

2. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 1, characterized in that: In step S1, the tunnel control sliding interface is determined through the analysis of basic engineering parameters, and the tunnel plug length is initially estimated, including: Determine the tunnel plugging design level and flood control standards according to the relevant hydraulic tunnel design specifications; Determine the controlled sliding interface of the tunnel: For unlined tunnels, the interface between concrete and surrounding rock is used as the controlled sliding interface; for lined tunnels, the fixed value method is used to calculate the anti-sliding stability of the interface between the plug and concrete as the sliding surface and the interface between concrete and surrounding rock as the sliding surface under the most unfavorable working conditions, and the controlled sliding interface is determined based on the anti-sliding stability; Combined with the design parameter values ​​of tunnel plugging design level and flood control standard and the controlling sliding interface, the partial factor limit state design method is adopted to estimate the tunnel plugging length.

3. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 1 is characterized in that: In step S2, the established risk model for the anti-sliding stability failure of tunnel plugging during the main flood season of ultra-high dam construction is: R=P(P H (max(Z m (t)))>f'∑W+C'(λA1+A2)) Among them, R represents the risk of failure of anti-sliding stability of tunnel plugging during the main flood season of ultra-high dam construction; Z m (t) represents the dynamic change process of the water level of the reservoir in front of the dam during the main flood season; P H (max(Z m (t))) is the thrust of the water load generated by the highest flood level on the upstream face of the plug; f' is the shear friction coefficient between the plug and the surrounding rock; ∑W is the sum of all normal forces on the control sliding surface; C' is the cohesion between the plug and concrete or between concrete and surrounding rock; λ is the effective bonding area coefficient of the side wall; A1 is the effective shear surface contact area of ​​the side wall; A2 is the effective shear surface contact area of ​​the bottom surface; P(·) represents the probability that the (·) condition is met.

4. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 1 is characterized in that: In step S3, the distribution parameters of the main random factors affecting the water load are determined to include: The construction flood peak is assumed to follow the P-III type distribution; The discharge capacity coefficient of the diversion tunnel is assumed to follow a triangular distribution; The water level-reservoir capacity relationship coefficient is assumed to obey a triangular distribution.

5. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 4 is characterized in that: In step S4, the distribution parameters of the main random factors affecting the anti-slip force are determined, including: The effective bonding area coefficient of the side wall is assumed to obey a triangular distribution, and its probability density function is: Among them, k d is the lower limit, i.e. the minimum effective bonding area coefficient of the side wall; k m is the median value, estimated based on the technical level of the construction unit and on-site management; k u is the upper limit value, i.e. the maximum bonding effective area coefficient of the side wall; The shear friction coefficient and cohesion of the plug material are assumed to obey the normal distribution, and their probability density functions are: Wherein, μ is the mean of the random variable parameter of the shear friction coefficient f' or the cohesion C'; σ is the standard deviation of the random variable parameter of the shear friction coefficient f' or the cohesion C'.

6. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 5, characterized in that: In step S5, based on the initially proposed tunnel plug length and in combination with the distribution parameters of the main random factors affecting the water load and the anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is performed, including: First, the total number of model simulation calculations N that meets the calculation accuracy requirements is determined based on the Monte Carlo method. C ; Then, combining the distribution parameters of the main random factors affecting water load and anti-sliding force, N C Random simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plug.

7. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 6, characterized in that: The random simulation process of the water load generated by the highest flood level of the dam during the main flood season includes: ① Generate random numbers of construction flood peaks to simulate the construction flood process; ② Generate random numbers of reservoir capacity relationship coefficients and simulate and fit the water level capacity relationship curve; ③ Generate random numbers of discharge capacity coefficients and simulate and fit the diversion and discharge capacity curve; ④ The maximum flood level in front of the dam during the main flood season is obtained by simulating flood control calculations. m (t)); ⑤ Calculate the water load P by simulating the highest flood level in front of the dam during the main flood season H (max(Z m (t))).

8. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 7, characterized in that: The random simulation process of the total anti-sliding force that the tunnel plug can generate includes: ① Generate a random number for the bonding effective area coefficient λ of the side wall; ② Generate random numbers of shear friction coefficient f' and cohesion C'; ③ Calculate the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate.

9. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 1, characterized in that: In step S6, based on the random simulation results, the risk rate of failure of the tunnel plugging anti-sliding stability during the main flood season of the ultra-high dam construction is estimated, including: According to N C The simulation results of random simulation of the water load generated by the highest flood level of the dam during the secondary flood season and the total anti-sliding force generated by the tunnel plugging are analyzed statistically. The water load P of the highest flood level in front of the dam is H (max(Z m The number of times (t))) exceeds the total anti-sliding force f'∑W+C'(λA1+A2)) that the tunnel plug can generate is recorded as N T ; According to Estimate the risk rate R of anti-sliding stability failure of tunnel plugs during the main flood season of ultra-high dam construction.

10. The method for optimizing the length of tunnel plugs during the main flood season of ultra-high dam construction according to claim 9, characterized in that: In step S7, according to the estimated risk rate of failure of the tunnel plugging anti-sliding stability during the main flood season of the ultra-high dam construction, the length of the tunnel plugging is optimized until the convergence condition is met, including: Determine whether the estimated risk rate R of tunnel plugging anti-sliding stability failure during the main flood season of ultra-high dam construction meets the following requirements: 0≤|R-R A |≤ε Among them, R A is the design risk rate, R A =1 / T A , T A is the flood return period corresponding to the tunnel plugging design standard; ε is the set convergence threshold; If satisfied, the optimization design process is terminated; otherwise, the length of the tunnel plug is adjusted. Based on the adjusted length of the tunnel plug and the distribution parameters of the main random factors affecting water load and anti-sliding force, a random simulation of the water load generated by the highest flood level of the dam during the main flood season and the total anti-sliding force that the tunnel plug can generate is performed again, and then the process returns to step S6.

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